Lipids can become rancid as a result of oxidation. This rancidity caused by oxidation is a major cause of food deterioration. The acceptability of a food product often depends on the extent to which such deterioration has occurred. Moreover, there is increasing evidence of a pathogenic role of endogenous lipid oxidation in a number of chronic and acute disease states. For instance, the association between high-fat diets and chronic diseases such as heart disease are well known. As a result, techniques for assessing the extent of oxidation of foodstuffs have been developed. Sensory analysis, e.g. taste or smell, is one of the most sensitive methods available for detecting lipid oxidation in food which results in rancidity. However, this method has not been practical for routine analysis. As a result, many chemical and physical techniques have been devised in an effort to quantify oxidative deterioration and to correlate the data with, for example, off-flavor development. Chemical methods include those which measure peroxide value, the thiobarbituric test, the Kreis test, those which measure total and volatile carbonyl compounds, and oxirane determination tests. Chromatography based on the physiochemical principles of adsorption, partition, ion exchange, or exclusion, or a combination of these principles, and mass spectroscopy have also been employed. A more complete review of these various methods for measuring the extent of oxidation can be found in Gray (J Amer. Oil Chem. Soc. 55:539-546 (1978)). However, many of the existing chemical methods employ high temperature, or strong acid or solution, which classify them as destructive methods and therefore require the commitment of a certain portion of the food as a loss.
Moreover, these conventional methods all suffer from several common disadvantages. For instance, one such disadvantage is that it usually takes an appreciable amount of time to perform most conventional tests on the sample, the length of time being dependent on the complexity of the test. This time delay between when the sample is taken and when the analysis is completed provides a window during which the food's content may have changed, leading to erroneous test results and can be especially troublesome when the time delay is lengthy.
Additionally, situations arise wherein repeated monitoring is desirable, such as, for example, when monitoring daily changes in the freshness of refrigerated meats and the like. Similarly, continuous measurements can be desirable in monitoring the cooking or other preparatory steps in food processing. In such instances, each of the factors of time delay and destruction of the sample (if required for the particular test procedure employed) can be disadvantageous as described above.
In the absence of reliable and rapid measurement techniques, wholesome foodstuffs often must be destroyed because arbitrary shelf-life or refrigeration limitations have expired. Likewise, in the absence of careful attention, foods can be ruined due to overcooking or other errors during processing.